I checked out the "other" adblock, distributed by linkz.com. if you read their user agreement, you'll see that in addition to blocking popups and ads, their software hijacks your browser to their proprietary search engine whenever you'd normally get a "url not found" type error. in other words, a commercial scam masquerading as an ad-blocker.

btw, there's a potential lawsuit for trademark infringement here, if your adblock came before theirs.

jiro:
Yea, but theirs is free too :P
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Also, their user-agreement spells the name AD-BLOCK. We've changed our name a bit, as well -- starting out AdBlock, but now lowercasing the 'b'. I think theirs came after ours, but I can't be sure.. and, in the end, the only concessions would be courtesy.

I haven't used their software, so I can't tell if it really messes with stuff, or just quietly "helps", as they claim. But, it's clearly standalone software, being managed from the "Add/Remove" control-panel.
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We have a dependancy on the browser. Technically, we're "The Adblock Project", and our product is "Adblock for Mozilla".